The U.S. Environmental Protection Agency is launching an investigation of the former Parkton landfill in northern Baltimore County for possible toxic waste contamination.

"Basically, we have reason to believe contaminants may exist around the landfill as a result of [conflicting] test samplings done there by residents and the state," said Michael Taurino, Maryland project officer for the EPA.

The move came after the EPA found fault with the analysis performed by the Maryland Department of the Environment.

If significant levels of toxic chemicals are found in the landfill, the site could be a candidate for the EPA's Superfund cleanup money.

Area residents called the EPA's action a victory in their three-year battle for a thorough investigation and cleanup of the landfill. They have long suspected that carcinogens illegally dumped at the landfill have been leaking from the site, contaminating ground water and threatening their wells.

State environmental officials disagree. They say that the contaminants found by residents in private wells are coming not from the landfill but from an outside source. And they staunchly defend their test results.

The EPA got involved this year when Dr. Richard McQuaid, a chemist and president of the Maryland Line Area Association, sent the federal agency the state's analysis of monitoring well samples taken in 1990 and 1992. Dr. McQuaid contended that the state had changed its analysis to a less-sensitive method that might not detect the presence of some contaminants.

The EPA concurred. Mr. Taurino said the EPA ordered the state early this summer to recompute its 1992 analysis "because we weren't pleased with the state's testing methods and we wanted to get a better grasp of just what we were dealing with at the landfill."

But Mr. Taurino said his agency's critique of the state tests "isn't that big of a deal because we have now launched a full-scale investigation of the site. So what the state did before doesn't matter that much anyway. The state has been very cooperative."

Mike Sullivan, a spokesman for the state Department of the Environment, said the agency received a letter from the EPA saying it wanted the state to do further testing, but "it didn't indicate that the EPA was unsatisfied with our results."

"The only thing I'm aware of is that EPA felt our detection level for lead hadn't gone far enough," said Mr. Sullivan.

Mr. Taurino said the investigation, which would be handled by the state environmental agency and overseen by the EPA, "will ** be a long project with a lot of test sampling still to go."

The landfill is north of Parkton and just east of Interstate 83 between the expressway and Downes Road. Baltimore County first applied to the state for a permit to use the 217-acre site in 1972, and the landfill opened in 1978 after a long legal battle with residents.

The material buried in the landfill came from the county's Resource Recovery Facility near Cockeysville. After ferrous metals were removed, the rest of the refuse was shredded and hauled to the Parkton landfill. The county closed the landfill in late 1982 after it reached capacity.

The ground water beneath the landfill enters the Fourth Mine Branch stream, which divides the site and ultimately empties into the Gunpowder River.

Several years ago, monitoring found the underground steel tanks used to collect the leachate beneath the landfill had corroded and leaked. The county had to replace the tanks with lined sump reservoirs.

Leachate is the liquid that results after rainwater works its way through the materials buried in the landfill. The leachate includes any contaminants contained in the buried material.

"We think we have an accurate picture of the contaminates contained in the leachate as we have been testing the monitoring wells since 1975," said Mr. Sullivan.

The community's test, conducted by a private, state-certified laboratory, were done on residential wells in the area, Dr. McQuaid said. Private wells are the only source of water in northern Baltimore County.

"I'm not trying to pick fights with anyone; I just want to protect our community and get this landfill cleaned up," Dr. McQuaid said.

The state still denies that there's any new contamination. "The only contamination we have found that can be linked directly to the landfill is the leachate that had leaked from several years ago," said Mr. Sullivan.

Dr. McQuaid dismissed the criticism thrown at the community's position. "Because the EPA is on their backs, the state and the county are circling the wagons," he said.